(1) Technical Field of the Invention
The present invention relates to antennas and more particularly, to amphibious antennas for providing Near Vertical Incidence Skywave (NVIS) communication.
(2) Description of the Prior Art
Tactical communications in the frequency range of 2–30 MHz take advantage of ionospheric propagation effects to gather or disseminate intelligence over large distances. In the 2–12 MHz range, one mode of ionospheric propagation (i.e., Near Vertical Incidence Skywave (NVIS)) is used for distances shorter than long haul ionospheric skip (less than 800 km), but longer than the “radio horizon” distance at these frequencies (greater than 40 km).
Antennas used for NVIS communications are typically large resonant wire structures of various forms that include inverted Vees or horizontal dipole arrays. Depending on the frequency of operation, the beam patterns of these antennas are distinguished by a lobe that points directly over head (zenith) in order to affect NVIS mode communications.
There is a need for NVIS communication capabilities over sea as well as over land. Moreover, there is a need for an antenna structure that is collapsible, compact, and portable.